The krisview DDV-7001 digital door viewer is a security device in the form of a doorbell and camera that is equipped with an LCD screen. This door viewer is useful for knowing who is knocking or pressing the doorbell of a house, before you open the door. You can see clearly on the LCD monitor that the guest is behind the door of the house. Digital door viewer uses a type of AA battery with a screen of 3.5 inches.